1. Field of the Invention
The present invention pertains to valves used in fluid flow applications and more particularly to valves used in fluid flow applications where the direction of flow must be controlled in addition to controlling the degree of fluid flow.
2. Related Art
In the area of transporting fluids from one location to another there are many situations where the flow of fluid must be free but only in one direction. This situation can occur whether the fluid flow is a hydrocarbon fluid, such as oil, or other fluids, natural gas, compressed air, such as fresh water. This can occur when transferring oil to or from tankers from or to tanks or transferring fresh water to a tank to dilute sewage. In any of these situations fluid flow is to be in only one direction and reverse flow can be anything from undesirable to dangerous. In other words, the fluid flow must flow only in one direction when the control valve restricting flow is opened. In most prior art applications, multiple valves, one fluid flow rate control valve and one check valve are used. In applications where the fluid flow can be in either direction, but only one direction at a time, a total of four valves, two flow rate control valves and two check valves are used. In some applications, two flow rate control valves and one gate valve are used. There are some combination gate and check valve devices that may be used, however, these arrangements are complicated and require two combination valves if fluid is to flow in either direction at specified times.
Presently, fluid flow control, specifically in oil fields, is performed by filing pipelines and various tanks and tank trucks using several different types of valve systems. In most instances, when fluid is being transferred from one location to another it is undesirable to have the flow reverse and backwash to the source. This is true whether transferring hydrocarbon fluids or water. Water being transferred may be fresh water and pumped into a tank or container having water of a different type, such as salt water, etc. To prevent reverse flow or backwash from occurring, a check valve is used in conjunction with the control valve that controls the rate of fluid flow. The check valve usually takes the form of a plate that swings out of the way when fluid is flowing in the desired direction. The plate swings shut when the fluid flow is reversed. To reverse the flow, the first valve is closed and a bypass valve that is connected around the two ends of the main valve is opened. This additional control valve may also be used in conjunction with a check valve to prevent backwash in the opposite direction.
This arrangement requires two fluid control valves, two check valves along with the requisite flanges, welds or other connections to ensure the integrity of the system.
An example of a ball valve being used a flow control valve is illustrated in U.S. Pat. No. 4,385,747, titled "Self-Relieving Seat and Ball Valve Incorporating the Same" issued to Paul Renaud, Jr. et al. This valve relates to an annular seat for use in a ball valve which has two groups of pressure relief passageways, each of which extends completely through the seat between its front and rear faces. This patent relates to a typical ball valve for controlling fluid flow with the addition of spaced ball valve seat rings to prevent back flow leakage through the use of the elastomeric valve seat rings.
An example of a check valve is illustrated in U.S. Pat. No. 4,437,485, titled "Check Valve" issued to Robert B. Goodman. This check valve includes a pair of valve elements. The first valve element is unseated during forward flow and is seated or checked by reverse flow. The second valve element is unseated by reverse flow, allowing the flow to reach the first valve element to aid in its seating for reverse flow.
U.S. Pat. No. 4,781,213, titled "Ball Check Valve" relates to a check valve which includes a chamber having two ports, and a central housing in which a ball moves freely from one port to the other and an elastomeric O ring is free to move transversely to the direction of travel of the ball. During forward flow, the ball does not impede the fluid flow. During reverse flow, the ball seats on the elastomeric O ring and closes off fluid flow.
Other examples of ball and check valves are contained in U.S. Pat. No. 4,543,986, titled "Ball Check Valve and Plate", 4,846,221 titled "Ball Valve with Built-In Check Valve", and 5,373,868 titled "Ball Valve with Modular Check Valve Assembly and Access Port".
A bidirectional control valve is generally illustrated in U.S. Pat. No. 5,174,544, titled "Normally Closed Pilot Operated Bi-Directional Poppet Valve". The valve of this patent relates to a normally closed pilot operated bidirectional poppet valve for controlling flow between first and second valve ports. When the pilot valve is closed, pressure is applied from whichever port is at the higher pressure to the poppet in a manner to hold the poppet closed. When the pilot valve is open, pressure is vented to whichever port is at the lower pressure in a manner to allow the poppet to open. Another example of a bidirectional valve is illustrated in U.S. Pat. No. 5,072,752 titled "Bidirectional Cartridge Valve".
As can be seen from the foregoing examples, there is nothing in the art that permits a simple, efficient valve system which allows controlled forward flow in either of two directions while preventing reverse flow in both cases.
Further, in many situations, the flow line must be pigged. In this process a Styrofoam plug or umbrella like device is run through the pipe line or flow line. This device is used to force out any moisture which has accumulated or any other impurity which may have settled in the line. It may also be used to carry a detector or other instrument to determine line integrity or potential structure defects. In either case, the device must fit tightly against the sides of the line. A line having any of the valves currently in use cannot be pigged in both directions or in some cases, cannot be pigged at all. This results in very costly procedures to clean or pig the lines where a valve is situated. In cases where lines cannot be pigged, defects cannot be detected until failure, which can be very costly, not only financially but also costly to the environment.